1. Technical Field
The invention relates to an optical device provided with a variable wavelength interference filter for taking out light with a predetermined wavelength from incident light.
2. Related Art
In the past, there has been known an interference filter having a pair of reflecting films opposed to each other, and for transmitting or reflecting only the light with a predetermined wavelength, which is reinforced due to multiple interference by the pair of reflecting films, out of the incident light, and further, there has been known an optical device for imaging the light transmitted through such an interference filter with an image sensor (see, e.g., JP-A-2000-162043 (Document 1)).
The optical device described in Document 1 is a device for collimating the incident light such as the light from an object with an objective lens, inputting the light thus collimated vertically to a variable wavelength interference filter, and receiving and then imaging the light transmitted through the variable wavelength interference filter with an image sensor.
In such an optical device, it is required to improve the resolution of the variable wavelength interference filter in order for receiving the light with a target wavelength using the image sensor. As such a variable wavelength interference filter, there can be cited, for example, a filter shown in JP-A-2009-251105 (Document 2).
The variable wavelength interference filer described in Document 2 has a pair of substrates opposed to each other, and one of the substrates is provided with a movable section and a diaphragm for holding the movable section so as to be able to move back and forth with respect to the other of the substrates. Further, the movable section is provided with one of the pair of reflecting films, and the other of the substrates not provided with the movable section is provided with the other of the reflecting films opposed to the reflecting film of the movable section. In such an optical filter device, the dimension of the gap between the pair of reflecting films can be varied by moving back and forth the movable section to thereby make it possible to take out the light corresponding to the dimension of the gap, and at the same time, since an amount of deflection of the movable section with respect to the diaphragm is reduced, it becomes possible to suppress also the deflection of the reflecting film provided to the movable section.
Incidentally, in Document 2, since the movable section is formed to have a thickness dimension larger than that of the diaphragm, it is possible to make the deflection amount of the movable section smaller than the deflection amount of the diaphragm even in the case in which the movable section is displaced. However, in reality, the deflection is also caused in the movable section, and the deflection amount is small in the central portion of the movable section, and increases as the position moves from the center toward the periphery of the movable section. Further, the deflection amount is also affected by the size of the variable wavelength interference filter, if the size of the variable wavelength interference filter is large, for example, the deflection amount of the movable section becomes also large. Therefore, since the deflection is also caused in the reflecting film disposed on the movable section, and the dimension of the gap between the pair of reflecting films fails to be uniform, the resolution is degraded.
Therefore, in the optical device described in Document 1, if the variable wavelength interference filter described above is used, there arises a problem that the measurement accuracy is degraded due to the degradation of the resolution in the variable wavelength interference filter. Further, although it is possible to obtain an image with higher resolution by increasing the size of the image sensor, on this occasion, it is required to also increase the size of the variable wavelength interference filter. However, as described above, if the size of the variable wavelength interference filter is increased, there arises a problem that the deflection amount of the movable section increases to thereby degrade the resolution, and thus the measurement accuracy is degraded.